pw_bluetooth_sapphire: Reorganize StopAdvertising calls

StartAdvertising(...) and StopAdvertising(id) both call generic
logic that is implemented in StartAdvertisingInternal(...) and
StopAdvertisingInternal(id) methods.

The no-arguments version of StopAdvertising() (intended for
stopping all all active advertisements), however, calls a
StopAdvertising() method in its superclass explicitly.

This inconsistency makes it a bit confusing to follow the logic,
so I added a StopAdvertisingInternal() implementation that follows
the pattern set by StartAdvertising(...) and StopAdvertising(id).

Test: pw presubmit --step gn_chre_googletest_nanopb_sapphire_build
Change-Id: I875f74409d02e8f8685604d722da83d8fade80e8
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/302392
Reviewed-by: Ben Lawson <benlawson@google.com>
Commit-Queue: Josh Conner <joshconner@google.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Docs-Not-Needed: Josh Conner <joshconner@google.com>
Tests-Not-Needed: Ben Lawson <benlawson@google.com>